The present invention relates generally to electrical switchboards and particularly to improved drawout apparatus for incorporation therein.
Prior art manually operated drawout apparatus have typically utilized various forms of camming mechanisms to achieve sufficient mechanical advantage requisite to overcoming the considerable contact pressures involved in mating and unmating the primary disconnects as the drawout device is manually racked between its engaged and disengaged positions. To minimize skewing of the device during this racking movement, the camming mechanism normally utilizes pairs of co-acting camming elements, stationed on opposite sides of the device, operating to develop parallel forces motivating the device between its engaged and disengaged positions. This approach is somewhat complex and costly, particularly since rather stringent manufacturing tolerances are required to insure that the racking forces are developed uniformly so that the device is racked smoothly between its engaged and disengaged positions in non-binding, unskewed fashion. Another consideration applicable to prior art drawout camming mechanisms is that there is typically a degree of play inherent in the co-acting camming elements when the direction of racking movement is reversed. Thus, when the device is racked to its fully engaged position, it is not fixedly secured thereat by the camming elements. Consequently, the electromotive forces associated with high fault currents flowing through the primary disconnects and, if the device is a circuit breaker, the gaseous high pressure exhaust emanating therefrom during a high fault current interruption develop considerable blowout forces acting to drive the device away from its fully engaged position. These blowout forces are not immediately resisted by the camming elements. To remedy this situation, a special latch has been utilized to securely hold the device in its fully engaged position, as disclosed and claimed in commonly assigned U.S. Pat. No. 4,202,027.
It is accordingly an object of the present invention to provide an improved switchboard drawout apparatus.
A further object is to provide drawout apparatus of the above character which is uniquely structured to achieve uniform and smooth racking movement of an electrical device as its primary disconnects are mated and unmated with associated switchboard primary disconnects.
An additional object is to provide a drawout mechanism of the above character which is inherently structured to securely retain the device in its fully engaged position.
Another object is to provide drawout apparatus of the above character which incorporates improved interlocking provisions to insure that the electrical device is in its off or open circuit condition while the primary disconnects are being mated and unmated.
Yet another object is provide drawout apparatus of the above character which is efficient in construction, inexpensive to manufacture, reliable in operation and both convenient and safe to use.
Other objects of the invention will in part be obvious and in part appear hereinafter.